The present invention relates to insulation for preventing strand-to-strand contact in high-voltage coils, and more particularly to an insulation insert for preventing electrical shorts and/or arcing in high-voltage stator coils.
Stator coils used in modem generators, such as the ones illustrated in FIG. 1, are typically manufactured using a technique referred to as Roebelling to improve the electrical performance of the individual copper strands that make up a stator coil. Roebelling involves transpositioning of the individual copper stands in a stator coil, as illustrated in FIG. 2, to vary the radial position of each copper strand over the axial length of the stator coil. Without such transpositioning, copper strands closer the center of a generator would be subjected to higher magnetic flux densities, and thus higher temperatures and loses, than those located further from the center of the generator. By transpositioning the copper strands, Roebelling helps insure that each copper strand in a stator coil is exposed to comparable magnetic flux and temperature conditions.
In order to transpose the copper strands in a stator coil, one or more crimps or bends must be placed in each of the individual copper strands. A number of techniques exist for forming such crimps. One such technique, known as 3D-crimping, utilizes a three-dimensional crimp configuration like the one illustrated in FIGS. 3A and 3B.
FIGS. 3A and 3B illustrate two copper strands 32 that have been crimped using the 3D-crimping technique. The crimped-copper strands 32 include a number of individual crimps 34. These crimps 34 may be formed, for example, using a crimping fixture having a crimping die and an actuator. Once crimped, the copper strands 32 are assembled to form a transposed stator coil as illustrated in FIG. 3B.
In their assembled state, the copper strands 32 are packed closely together. Therefore, adjacent copper strands may contact each other or come into close proximity of each other. To prevent electrical shorts and/or arcing between adjacent copper strands, manufactures generally purchase and utilize copper strands that have been pre-coated with one or more thin layers of insulation coatings.
One problem with this appoach is that the insulation coatings are frequently damaged during the crimping process. If an insulation coating on a copper stand is damaged, the bare copper of the copper strands may be exposed, which may lead to electrical shorts and/or arcing between adjacent copper strands. The problem is made worse in 3D-crimp configurations because, as illustrated in FIGS. 3A and 3B, the crimps in one copper strand tend to line up with the crimps in an adjacent copper strand. Thus, electrical contact and/or arcing between adjacent strands is even more likely.
In an effort to overcome the problem described above, manufacturers often add an additional durable-varnish-insulation coating to the copper strands before assembly and crimping. This durable-varnish-insulation coating tends to withstand the crimping process. However, it also adds significant cost to the end product.
With the above in mind, an insulation insert consistent with the present invention is described that effectively prevents electrical shorts and/or arcing between adjacent copper stands, but significantly reduces the costs associated with conventional techniques.
An insulation insert consistent with the present invention is provided for preventing electrical shorts and/or arcing between adjacent strands in a stator coil. The insulation insert includes a thin base of substantially uniform cross section and a lead-in nose formed in the thin base for guiding the insulation insert into a position between adjacent strands. The insulation insert includes two substantially vertical cuts in the base above the lead-in nose, which delineate a center section flanked by two ear portions. The center section may be formed into a head by horizontally folding the center section at a point midway along the vertical cuts. The insulation insert may also include a substantially horizontal cut in each of said ear portions to facilitate bending of said ear portions in opposite directions to form opposing wings in said insulation insert.